Sean Raggett's first-half goal gave Rotherham an important 1-0 Sky Bet Championship win over Millwall at the AESSEAL New York Stadium.
Raggett, on a season-long loan from Norwich, headed home in the 20th minute and that proved enough for the Millers to earn their second victory of the season in awful Bank Holiday conditions.
That leaves the Millers, who were promoted from League One last season, with six points from their opening five games.
It continued a miserable week in South Yorkshire for Millwall as this followed up a midweek loss at Sheffield Wednesday, though they fashioned enough chances to maybe have earned a draw.
Set-pieces have been Rotherham's biggest threat this season and so it proved again as, after a non-descript start, they took a 20th-minute lead.
A short throw-in was played back to Will Vaulks and his precise cross was headed home by Raggett for his first league goal for the Millers.
That opened the game up and the hosts continued to pose more problems as a wicked free-kick from Ryan Manning just avoided Richard Wood at the far post, while Ryan Williams drove over from the edge of the area.
Their best chance to add a second before the break came from the second phase of a corner when the ball ended up with Semi Ajayi at the far post but he put his shot into the side-netting.
Millwall came out on a mission in the second half and almost levelled in the 55th minute but Jake Cooper's powerful header from Shaun Williams' corner.
Rotherham began to get a foothold in the game again and after Ryan Williams and Manning had gone off target they should have doubled their lead on the hour.
Michael Smith's superb chest down set Kyle Vassell free and he returned the ball to Smith, whose low effort from 10 yards was saved by Jordan Archer.
The Millwall response came and they had chances to get back level, but Tom Elliott's low shot was saved by the feet of Marek Rodak, while #1million man Tom Bradshaw, making his debut following his move from Barnsley headed over.
Jed Wallace was Millwall's biggest threat throughout the game and he came closest to levelling in the final 10 minutes.
The midfielder was afforded too much space outside the area and he unleashed a wicked drive that flew inches wide of Rodak's post.
With that went the Lions' last chance and the Millers held on for a vital win.